Painting by Konstantin Altunin of Vladimir Putin and Dmitry Medvedev in womens underwear.

A painting depicting politicians Vladimir Putin and Dmitry Medvedev in women’s underwear was one of the items Russian authorities confiscated Monday upon raiding a newly-opened St. Petersburg art gallery that had shown solidarity with Russia’s gay-rights movement.

The off-beat gallery, known as the Museum of Authority, opened on August 15 with an inaugural exhibit called “The Rulers” that featured paintings by artist Konstantin Altunin of public figures such as President Barack Obama, former Libyan leader Moammar Gadhafi and Mr. Putin. The idea of the museum had been to put on exhibits relating to various authorities, said founder Alexander Donskoi.

Much of the inaugural exhibit was raunchy or politically-charged. One painting depicted St. Petersburg politician Vitaly Milonov – who spearheaded a local “gay propaganda” law that became inspiration for similar national legislation – against a rainbow background. The law bans people from expressing support for “non-traditional” lifestyles in front of minors. A national version of it was signed into law in June.

Mr. Milonov accompanied police at the gallery, according to Mr. Donskoi. The officers confiscated the portrait of Mr. Milonov – which was hanging on the wall between two sexually-explicit paintings, according to photos – as well as the painting depicting Messrs. Putin and Medvedev in women’s underwear.

Authorities also took two other works of art. One was a painting of Russian Orthodox Patriarch Kirill with criminal-style tattoos mixing Soviet and religious iconography. The other was one of Yelena Mizulina, the Kremlin-allied Duma deputy and morality crusader who led the drive to pass Russia’s “gay propaganda” law nationally. That painting was entitled “The Erotic Dreams of Deputy Mizulina.”

Mr. Milonov couldn’t immediately be reached for comment.

In a statement on its website, the St. Petersburg branch of Russia’s Interior Ministry said it had dispatched officers to the museum on Monday after someone complained that the gallery’s contents may be illegal. “Following an initial inspection, police seized four paintings that have been sent off for analysis, on the basis of which a procedural decision will be made,” the statement said.

The Interior Ministry statement did not say anything about closing the museum, but Mr. Donskoi says it has been closed down and won’t reopen. A video on the museum’s Russian social-networking page shows a police officer sealing shut the door to the gallery.

Last weekend, the museum offered free entry “in solidarity with Russia’s LGBT community.” The “password” to gain free admission was for people to say they were gay, lesbian, bisexual or transgendered at the door. The issue has come to the fore amid calls by some Western activists for a boycott of the 2014 Winter Olympics in Sochi due to the new “gay propaganda” law.

Mr. Donskoi said there were warnings on the exhibition so that minors wouldn’t enter. He also said there were messages warning people whose religious beliefs might be offended not to come inside. In addition to passing the gay-propaganda law earlier this year, Russia’s parliament also passed a law criminalizing public actions that “insult the religious feelings of the faithful.”

Mr. Donskoi isn’t new to controversy. He was the mayor of Russia’s northern city of Arkhangelsk from 2005 to 2007 but faced criminal charges after announcing plans to run in the 2008 presidential election. He was found guilty of abuse of office and given a suspended sentence. He says the charges were a trumped-up attempt to remove him from politics.

The former politician then went on to open a so-called museum of erotica in Moscow, as well as a USSR Museum with a fake corpse of Vladimir Lenin that looks like it is breathing. The Museum of Authority was his newest project—but he fears it may have gone too far.

Under new laws authorities could convict a person even for what he or she writes on a social networking website, Mr. Donskoi said. “I’m very afraid in this situation,” he said. “Because today the authorities can do whatever they want.”